1. Technical Field
The present specification relates to an image forming apparatus and a method for controlling the image forming apparatus, and more particularly, to an image forming apparatus and a method for controlling the image forming apparatus for detecting a shift in position of a recording head in a main scanning direction.
2. Discussion of the Background
An ink-jet recording apparatus, serving as an image forming apparatus, such as a copying machine, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, forms an image on a medium (e.g., a sheet) by discharging liquid.
The ink-jet recording apparatus includes an ink cartridge and a sub tank. The ink cartridge is provided in a device body, and mainly stores liquid (e.g., an ink) to be supplied to the sub tank. The sub tank is provided on a recording head, and temporarily stores ink supplied from the ink cartridge. The ink stored in the sub tank is supplied to the recording head. The recording head is carried by a carriage and discharges ink onto a conveyed sheet. The ink is adhered to the sheet to form an image on the sheet.
In order to maintain high image quality, stable ink discharge is needed. Thus, proper control of negative pressure inside the sub tank is important. In one example of a related art ink-jet recording apparatus, for example, an air intake valve opens to discharge a predetermined amount of air remaining in the sub tank, and the air intake valve closes to discharge a predetermined amount of ink. Therefore, a negative pressure generation mechanism in the sub tank functions to generate a predetermined negative pressure inside the sub tank.
The sub tank includes a film member forming an ink container. On the outer surface of the film member there is provided a negative pressure lever. The negative pressure lever may be displaced according to deformation of the film member.
In another example of a related art ink-jet recording apparatus, since negative pressure in the sub tank increases as an amount of ink in the sub tank decreases due to discharging of ink drops, when a predetermined amount of ink is consumed, ink is filled to prevent an excessive increase of negative pressure.
In order to provide a compact ink-jet recording apparatus, the carriage carrying the sub tank and the recording head is requested to be made more compact. Therefore, a shift amount of the negative pressure lever mounted on the carriage needs to be small, and thus, even a slight shift in a position of the negative pressure lever affects negative pressure in the sub tank.
Ink discharge depends on the precision with which the position of the negative pressure lever is detected. If the position of the negative pressure lever is not precisely detected, then when an ink supply operation is performed based on incorrect information about the position of the negative pressure lever ink might leak from the recording head because excessive ink is supplied to the sub tank, or, conversely, a faulty image may be formed due to insufficient ink.